Emergency Vehicle Traffic Signal Preemption System

ABSTRACT

An emergency vehicle traffic light preemption system for preemption of traffic lights at an intersection to allow safe passage of emergency vehicles. The system includes a real-time status monitor of an intersection which is relayed to a control module for transmission to emergency vehicles as well as to a central dispatch office. The system also provides for audio warnings at an intersection to protect pedestrians who may not be in a position to see visual warnings or for various reasons cannot hear the approach of emergency vehicles. A transponder mounted on an emergency vehicle provides autonomous control so the vehicle operator can attend to getting to an emergency and not be concerned with the operation of the system. Activation of a priority-code (i.e. Code- 3 ) situation provides communications with each intersection being approached by an emergency vehicle and indicates whether the intersection is preempted or if there is any conflict with other approaching emergency vehicles. On-board diagnostics handle various information including heading, speed, and acceleration sent to a control module which is transmitted to an intersection and which also simultaneously receives information regarding the status of an intersection. Real-time communications and operations software allow central and remote monitoring, logging, and command of intersections and vehicles.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is continuation of U.S. application Ser. No.10/811,075, filed on Mar. 24, 2004, which is a continuation-in-part ofU.S. application Ser. No. 10/642,435, filed Aug. 15, 2003, which claimsthe benefit of U.S. Provisional Application No. 60/403,916 filed Aug.15, 2002, the content of all of which are incorporated herein byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention described herein was made in the performance of work undera NASA contract, and is subject to the provisions of Public Law 96-517(35 U.S.C. § 202) in which the Contractor has elected to retain title.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to systems for controlling vehicle trafficsignals to allow safe passage of emergency vehicles and moreparticularly relates to a system for autonomously preempting trafficsignals at an intersection that includes a vehicle transponder, areal-time intersection controller and monitor (with anintersection-based visual and/or audio alarm warning system), anoperations display and control software, and a wide-area communicationsnetwork.

2. Background Information

Present systems used to preempt traffic signals and clear intersectionfor emergency vehicles responding to a life-saving event often come withsevere limitations. They rely on: sound activation, optical activation,direct microwave activation, and a combination of all the above. All ofthese systems have severe operational limitations affected by weather,line of sight, and critical range. These systems often have furtherdrawbacks requiring them to be activated by the emergency vehicleoperator or first responder (herein referred to as “e-operator”). Thesesystems also severely disrupt the normal phasing patterns of a trafficcontroller's nominal programming because these systems do not providereal-time monitoring of intersection phases or timing.

Emergency vehicles currently rely on vehicle horn, sirens, and flashinglights to prevent accidental collisions with pedestrians or othervehicles at intersections. E-operators must focus all their attention ondriving the vehicles. Other preemption systems fail to provide visual oraudio feedback systems (to either motorists or e-operators) that arephysically located in the intersection (herein referred to as“intersection-based warnings”). Such preemption systems compromisemotorist and e-operator safety, as there is no awareness of atraffic-light preemption event (referred herein as “silent preemption”).Additionally, these systems fail to provide real-time feedback toe-operators through warning devices inside their vehicles (hereinreferred to as “vehicle-based warnings”). These factors have the effectthat e-operators do not get the feedback required and soon stop usingthe system.

An intersection-based preemption system that provides feedback and isactivated autonomously by an approaching emergency vehicle is needed.Such a system overcomes some of the drawbacks of available systems.Intersection-based visual warnings are proven effective for motorists,and are also critically important to e-operators when multiple emergencyvehicles are approaching the same intersections (referred herein as“conflict detection”). These displays are directly in theirfield-of-vision and e-operators are immediately aware of potentialconflicts. Human factors studies often refer to such indicators as“real-world”. Intersection-based warnings combined with autonomousactivation removes the distraction by keeping drivers' eyes on the road.

A system is needed that takes special consideration of pedestrians.Visual intersection-based warnings may fail to get the attention ofpedestrians standing near an intersection. For this reason, audiblealerts in addition to visual may be the most effective (and rapid)warning system of the approach of emergency vehicles. There is also thedifficulty that pedestrians may often be in harms way if they fail tohear an approaching emergency vehicle. Although vehicle sirens areespecially loud, many circumstances can lead to dangerous situations andpotential injury. For instance, an especially long crosswalk may take upto 20 seconds to cross. In that time, an emergency vehicle may be heard,perhaps stranding the pedestrian in the middle of a crosswalk. Likewise,in extremely busy metropolitan intersections, ambient noise in thebuilding occlusions may prevent warning of the emergency vehicle untiljust seconds before the vehicle arrived at an intersection. A system isneeded that disables normal pedestrian clearance at intersections longbefore actual preemption has been triggered (herein referred to as“pedestrian-inhibit”). This system would greatly enhance the safety ofemergency vehicle preemption by preventing pedestrians from entering anintersection long before a vehicle arrives (or can be seen or heard).

Existing preemption systems provide little or no visibility,configuration control, or remote interaction with their operation orfunction. A system is needed that provides real-time feedback,monitoring, logging, and control of vehicle and intersectionpreemption-related data. This data would be displayed at both mobilestations and central operation center(s). Additionally, a system isneeded that provides secure, robust transfer of data to/fromintersections, vehicles, and operation center(s) using either wirelessor LAN architectures. All of these functions enable logisticalcommanders and traffic management authorities to coordinate, configure,and monitor activity in the overall preemption network.

It is one object of the present invention to provide an emergencyvehicle traffic signal preemption system that is fully autonomous andnot dependent on the intersection being in visual range.

Still another object of the present invention is to provide an emergencyvehicle traffic signal preemption system that includes a real-timemonitor of intersection phase to optimize triggers and timing for bothpreempt and pedestrian-inhibit functions. This includes minimizingdisruption of normal traffic controller behavior and sequencing.

Still another object of the present invention is to provide an emergencyvehicle traffic preemption system that includes visual displays in theintersections (and interfaces to such displays) indicating direction andlocation of approaching emergency vehicle(s).

Still another object of the present invention is to provide an emergencyvehicle traffic signal preemption system that provides conflictdetection (between emergency vehicles and e-operators) and alerts otheremergency vehicles in the area. This conflict detection is provided intwo forms: intersection-based warnings and vehicle-based warnings.

Still another object of the present invention is to provide an emergencyvehicle traffic signal preemption system that includes a pedestrianaudio warning signal to supplement the intersection-based visual displayand the audio signals from emergency vehicles.

Yet another object of the present invention is to provide an emergencyvehicle preemption system having an autonomous emergency vehicletransponder including an on-board diagnostic (OBD) interface, areal-time navigation interface and position estimation module, and acommunications monitor and control interface.

Still another object of the present invention is to provide an emergencyvehicle traffic signal preemption system that allows real-time remoteaccess, monitoring, and tracking of the entire preemption system viasecure wide-area networks (wireless and LAN). This includes access tothe operations display and control software (herein referred to as“operations software”) from management centers (TMC, 911-call center,etc.), mobile commanders, as well as individual emergency respondervehicles.

BRIEF DESCRIPTION OF THE INVENTION

The purpose of the present invention is to provide an improved emergencyvehicle traffic signal preemption system including autonomous operation,real-time phase monitoring and visual/audio signals to alert motoristsand pedestrians of the approach of emergency vehicles.

The system is fully autonomous and is not affected by range, weather, orline of sight. It provides real-time monitoring of the intersectionphases to optimize intersection timing and provide the visual display toalert motorist of oncoming emergency vehicle and the direction it iscoming from. This system is an improvement for use with the systemdisclosed and described in U.S. Pat. No. 4,704,610 of Smith et al issuedNov. 3, 1987 and incorporated herein by reference. The system alsoprovides an added feature of conflict indication inside the emergencyvehicle operator, indicating that another emergency vehicle isresponding and is approaching the same intersection, indicating whichvehicle has the preemption and right of way.

This system is unique in that it is fully autonomous and not dependenton the intersection being in visual range. It provides conflictdetection and alerts other emergency vehicle operators in the area, hasthe ability to interrupt pedestrian access, stops preemption when anemergency vehicle stops, and provides interface to and control of thesystem disclosed and described in the above-identified patent.

The improved emergency vehicle traffic signal preemption system consistsof three major subsystems. An intersection monitor and control, anemergency vehicle transponder and its interfaces, and a wide areacommunications network and its associated proprietary control programsoftware. The emergency vehicle intersection preemption design connectsintersections and vehicles over a two-way wide area wirelesscommunications network. This network is synchronized via GlobalPositioning System (GPS) timing signals. The system is also capable ofusing existing traffic management LAN networks to relay data tooperations center(s).

When an e-operator receives an emergency response request, the vehicleis placed in a priority-code (i.e. Code-3) mode with lights and sirensoperating. The vehicle emergency state is read via an emergency-codevehicle interface. At the same moment, the vehicle preemptiontransponder reads the vehicle on-board diagnostics (OBD) data anddetermines speed and acceleration, and gathers navigation data from oneof several navigation systems. This data is collected by an on-boardmicroprocessor that processes this information and predicts heading andposition. Estimation techniques include (but are not limited to) deadreckoning and position hysteresis—historical dependence—and aredependent on the sensor data quality. This information is thenformatted, the vehicle identification (ID) and absolute time added, andthe data is then transmitted to various both intersections and vehicleswithin the design area of coverage. The data is also immediatelyforwarded along the network to subscribing mobile and fixed operationscenter(s).

Intersection processors receive the data, identify the vehicle'sestimate-time-of-arrival (ETA), and compare it with other vehiclespossibly approaching their locations. It then determines which vehicleobtains highest priority (depending on location history, priority-typeof vehicle, and other factors). The processor sends notification to allapproaching emergency vehicles, warns of any potential conflict, andnotifies the local e-operators which vehicle has the right of way.

Simultaneously the processor collects real-time intersection phasing andtiming information and calculates when preemption should start based onthe vehicle(s) ETA. The system includes the real-time monitoring ofanalog, digital, and stand-alone (disabled monitoring) controllers. Thismonitoring optimizes preempt behavior and provides a closed-loopverification that preempt commands are executed by the intersectioncontroller.

It also calculates when to trigger the pedestrian-inhibit function toprevent clearance for crossing access. When preemption starts,intersection-based warning displays are sent coded commands via awireless or hard-line connection to light the proper icons. For eachdirection, the displays show all preempting emergency vehicles'direction and location, and light the appropriate emergency vehiclemessage (i.e. “Warning Emergency Vehicle”). All this takes place in realtime, in a manner appropriate to insure an intersection is preemptedearly enough for safe and clear access, and in such a way as tominimized speed reduction for the emergency vehicles.

The system disclosed herein provides a number of improvements of theabove-identified patent. It is an autonomous system that does not needinvolvement of emergency vehicle operator. It also includes expandedsystem capabilities using emergency vehicle on-board diagnostics (OBD),monitoring multiple emergency vehicles approaching the same intersectionusing Global Positioning System (GPS), and speed and heading informationfor multiple emergency vehicles to determine the right of way. Anintersection status is transmitted to emergency vehicle dashboardsindicating when the intersection is safe to traverse. A dashboarddisplay indicates to the vehicle operator the status of an intersection.The system is also capable of providing dynamic and customized displaysvia an interface to the vehicle-based PC (personal computer) systems.This interface provides detailed, real-time positioning and status ofall neighboring emergency vehicles and intersections. It allowse-operators to view maps with active vehicles and also allows forenhanced conflict detection notification. The system also includes awide area wireless RF communication links between emergency vehicles andintersections. This system is reliable and unaffected by weather, rain,or lack of line of sight.

Simultaneous to preemption triggers, pedestrian audio alerts areactivated when emergency vehicles are approaching an intersection. Theseare important because often visual signs at an intersection may not beclearly visible to a pedestrian. Beepers, bells, sirens, or even spokeninstructions at high volume can be used.

Several types of emergency vehicle location and navigation informationretrieval are possible. Among these are Global Positioning Systems(GPS), dead reckoning, beacon triangulation, tags, traffic loop, RDIF,etc. Each vehicle has an identification (ID) tag that allowstransmission to the appropriate vehicle that it has the right-of-way toa preempted intersection.

The improvements to the existing system in the above-identified patentare to enhance the performance but the purpose of the system remains thesame. That is, to alert and stop vehicles and pedestrians from using anintersection and to allow an emergency vehicle to pass safely. Someprior warning is necessary to allow clearing the intersection. Theprevious implementation uses a one-way infrared link to transmitapproach and departure information of emergency vehicle to theintersection which is equipped with four emergency vehicle statusdisplay panels mounted next to the usual traffic lights at eachintersection.

The system transmits a signal causing all traffic lights at anintersection to switch to “red” thus stopping all traffic in alldirections. In addition, the display panels flash a relatively large“emergency vehicle” therein with a graphic display indicating the laneand direction of traffic taken by an emergency vehicle. The range of theinfrared transmitter can be as much as 1,000 feet allowing sufficienttime to clear the intersection. The new improved system utilizes a widearea wireless RF two-way communication link between emergency vehiclesand intersections. This method is more reliable and not affected byweather, lack of line of sight, range limitation or obstructions.

Another advantage of the two-way wireless RF communications link betweenthe intersections and emergency vehicles is the ability to display muchmore useful data in the vehicles helping the vehicle operator maneuverhis vehicle most efficiently and safely. This data includes (but is notlimited to) emergency-code levels, vehicle acceleration, vehicle type,and vehicle health. This method also enables feedback communication tobe sent from the intersections to the vehicles, providing vehicle-basedwarnings (or confirmation) of system activity. Intersection “green”status shows when an intersection has been preempted and priority isgiven to the receiving vehicle, allowing safe passage. If more than oneemergency vehicle approaches an intersection, the system determineswhich vehicle should have the right of way depending on locationinformation (GPS, traffic loop, beacon, etc.), direction and speed sentto the intersection control. A proprietary control program determinesthe right of way and sends the result to emergency vehicles. Theencrypted data package transmitted over transceivers is tagged with thevehicle ID and time to insure proper and certified utilization.

Another improvement to the system is an audio warning system intended toalert pedestrians that an intersection has been preempted and must bekept clear. One desirable implementation would utilize loudspeakersmounted near the four corners of the intersection where pedestriansnormally gather to cross. A spoken message, such as “warning, emergencyvehicle approaching, do not walk”, may be most preferred but any audiblesignal such as a wailing sound, a siren, or any other familiar emergencysound may be utilized.

Another goal of the improved system is creation of an autonomous systemthat is activated by reception of a priority-code (i.e. Code-3) statusor alarm. The operator of the emergency vehicle can concentrate on hisprimary duty which is to arrive at the sight of the emergency safely inthe shortest time possible without worrying about the activation of thesystem. A priority-code starts the process of communication between anintersection that is being approached and the emergency vehicle and thesystem performs the functions described above. Also, both vehicle-basedwarnings and intersection-based warnings provide positive feedback thatan e-operator has secured an intersection. This directly translates intoa reduction of emergency workers' stress levels.

The information available from the emergency vehicle and intersectioncontrollers may be transmitted to a central location such as a dispatchcenter or traffic control center to display the status of multiplicityof intersections and emergency vehicles. Such information beingdisplayed on a status board can be invaluable in managing emergencysituations (especially large-scale incidents) in a more sufficientmanner because it makes available information on a real-time basis forthe officials in charge. Commands and configuration information can alsobe sent back to intersections and vehicles to instantly meet changingneeds or requirements. These instructions can include the creation oflarge emergency corridors (herein referred to as an “e-corridor”)whereby a series of sequential intersections are preempted in the samedirection.

The above and other objects, advantages, and novel features of theinvention will be more fully understood from the following detaileddescription and the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the functions of intersection hardware forthe emergency vehicle traffic signal preemption system (herein referredto as “preemption system”), as used for interfacing with allintersection controllers.

FIG. 2 is a block diagram of the functions in an emergency vehicletransponder for the preemption system.

FIG. 3 is an example schematic block diagram of a standard vehicletransponder for the preemption system.

FIG. 4 is an example schematic diagram of a vehicle on-board diagnostic(OBD) circuit for the preemption system.

FIG. 5 is a functional organizational diagram of the three majorsubsystems for the preemption system.

FIG. 6 is a schematic block diagram of the intersection hardware for thepreemption system, as configured for interfacing to an intersectioncontroller without monitoring.

FIG. 7 is a schematic block diagram of the intersection hardware for thepreemption system, as configured for interfacing to an intersectioncontroller with digital BUS monitoring.

FIG. 8 is a schematic block diagram of the intersection hardware for thepreemption system, as configured for interfacing to an intersectioncontroller with analog monitoring.

FIG. 9 is a general flow diagram of the intersection control programsoftware for the preemption system.

FIG. 10 is a general flow diagram of the vehicle transponder controlprogram software for the preemption system.

FIG. 11 is a detailed decision flow diagram of the preempt monitor taskcomponent for the intersection control program software.

FIG. 12 is a detailed time sequence diagram of the standard preemptioncriteria used by the intersection control program software in a typicalpreemption scenario.

FIG. 13 is a layout and topology diagram of the communications andoperations network for the preemption system.

FIG. 14 is a block diagram of the functions and data flow of theoperations software for the preemption system.

FIG. 15 is an example of the data status module display component andalerts module display component, used in the operations software for thepreemption system.

FIG. 16 is an example of the intersections module display component,used in the operations software for the preemption system.

FIG. 17 is an example of the vehicles module display component and themapping module display component, used in the operations software forthe preemption system.

DETAILED DESCRIPTION OF THE INVENTION

The three major subsystems in the emergency vehicle traffic signalpreemption system are shown in FIG. 5: the vehicle transponder 200, theintersection hardware 230, and the communications and operations network260.

The vehicle transponder 200 is composed of three main components. First,the vehicle computer interface module 205 includes the on-boarddiagnostics circuit and the emergency priority code interface. Second,the navigation predict module 210 uses navigation sensors such as GPSand INU (inertial NAV unit) sensors to generate both absolute andestimated dead reckoning position reports. Third, the transpondercontrol module 215 provides an interface to the e-operator via LEDs, PCdisplay, or PDA device.

The intersection hardware 230 is composed of three main components.First, the intersection monitor module 235 provides real-time readingand logging of controller signal and pedestrian phasing and timing.Second, the intersection control module 240 performs ETA calculationsusing vehicle positions and local known mapping topology (commonly knownas map-matching). This module also tracks and logs vehicles, actuatesand verifies preempt signals, manages communications between othernetworked units, and manages remotely-generated intersectionconfiguration commands. Third, the warning alerts control module 245actuates intersection-based visual and/or audio warnings. This modulealso ensures that warning alerts follow specific rules and timingparameters that govern the sequencing of warning signs with trafficlights.

The communications and operations network 260 is composed of three maincomponents. First, the slave (end-unit) transceivers in vehicles andintersections 275 relay the core preemption status and configurationdata to the backbone network. Second, the backbone wireless or LANnetwork 270 is a hybrid wide-area network designed to route data betweenmobile wireless vehicles, hard-lined and isolated wirelessintersections, and the central operation center(s). Third, theoperations software 265 provides for display of all real-time datagenerated by the intersections and vehicles including positions/speed,phasing, preemption-status, vehicle diagnostics, logged information,configuration data, and many other data parameters. This display/controlsoftware 265 can be mobilized for use in any management center, stagingarea, or even an entire fleet of emergency vehicles.

The functional details of the major subsystems in the emergency vehicletraffic signal preemption system are illustrated in the block diagramsof FIG. 1, FIG. 2, and FIG. 13. FIG. 1 illustrates the functionaldetails of the system at each intersection, FIG. 2 illustrates thefunctions of the system installed in an emergency vehicle, and FIG. 13illustrates the topology and display/control software used for thecommunications and operations network.

Traffic light control system 100 at an intersection includes trafficlight controller 20 (housed in cabinet 500) that generates theappropriate sequence of on-time and off-time for the various trafficlights that controls vehicular and pedestrian traffic at anintersection. Traffic light controller 20 also has the capability to beforced by external signals into a mode that activates “green” lights ina specified direction and “red” lights in all other directions, allowingsafe passage for emergency vehicles from the “green” direction.Controller 20 is preferably a micro-processing circuit driving isolatedlamp drivers but discrete designs are also feasible. Some intersectionsmay be more complicated, controlling turn lanes with arrow lights, butthe basic principles remain the same.

An example of an intersection being controlled by the system andfunctions disclosed and describe herein is shown in FIG. 1 of U.S. Pat.No. 4,704,610 referred to hereinabove and incorporated herein byreference. This figure shows the signage and approach of emergencyvehicles being controlled. The only feature missing is the pedestriancontrol signs at each corner which are an added feature of the inventiondisclosed and described herein.

Traffic light controller 20 generates signals to control pedestrianlights 22 a, 22 b, 22 c, and 22 d and also controls the operation oftraffic lights 24 a, 24 b, 24 c, and 24 d. An intersection havingtraffic lights can be connected to a system using the emergency vehiclepreemption system by addition of the functions described hereinafterwithout the need to rebuild an existing installation.

The heart of the additional equipment is the intersection controlmodule, a microprocessor 515 (e.g., a ZWorld LP 3100 CPU) operated byproprietary control program software 35. Controller 10 (housed inhardware module 510) receives information from emergency vehicles thatapproach an intersection via wireless RF transceiver 40 and antenna 41.This information contains data about the predicted position, heading,other navigation data of the emergency vehicle, and its priority-codestatus 36 (i.e. Code-3, Code-2, or other) thus notifying theintersection of its relative location.

FIG. 9 illustrates the general functionality of the intersection controlprogram software and firmware 35 (see Appendix B). The vehicle monitorsoftware task 605 running on the intersection CPU 515 tracks all localvehicles and maintains a log of all activity. The task also sendsconflict detection warnings, when appropriate, to the vehicles.

The intersection control program 35 continually evaluates its preemptionrules as vehicle updates are received. Position and priority parametersof each vehicle within range are analyzed by the intersection preemptmonitor software task 600. The primary decision logic of this task isillustrated in FIG. 11. Appendix A provides detailed explanations of theterms and parameters used in this figure and the description below. Thepreempt monitor task uses map-matching techniques to evaluate allvehicles against all eligible cross street segments 700 to determinewhich vehicles are inbound or outbound 730 from the intersection. Thetask assigns preemption priority to that vehicle which is withincritical perimeter zones (pedestrian 705 and preempt 706), in highpriority priority-code 710, and is a valid vehicle type 720. In order tooptimize the preemption process, it compares the minimum vehicle-ETAwith both the intersection clearance time (time-to-preempt) and aminimum complete-preemption time (threshold) 715.

FIG. 12 provides a visual illustration of the logic of the intersectionpreempt monitor software task. The diagram shows the actual positions(p_(#)) based in time along the actual path 621 of the vehicle. Forevery actual position (p_(#)), there is a same-time position report(e_(#)) along the estimated path 620 of the vehicle. For instance, p₁623 and e₁ 622 both occur at same time t₁. The diagram illustrates theestimate path 620 with valid position-lock (i.e. GPS occlusion), as wellas temporary loss of position-lock 624 when dead reckoning is used tocompensate. The diagram also illustrates the multiple uses of proximity(perimeter) layers, with a pedestrian-inhibit perimeter 625(“max-PED-perimeter”), a preemption-allowed perimeter 626(“max-preempt-perimeter”), a critical distance perimeter 627, andmultiple critical distance street segments 628. Non-critical segments636 are also shown (these street segments require additional evaluationbased on vehicle-ETA). The exit window 631 displays an example exitdistance range where egress intersection-based warnings are allowed tobe activated (based on configurable minimum and maximum exit distancecriteria). Also, the evaluation of vehicle heading compared against theroad heading is shown as the direction-error 622. The acceptabledeviation of the estimated position from the center-line of the street630 is also shown.

FIG. 12 also shows one of the more advanced preemption techniques usedon the intersection control program, the use of “threshold-lag” 640,641, and 642. “Threshold-lag” is defined in Appendix-A. In simple termsit is percentage error factor added to the threshold that gives the“benefit-of-the-doubt” to any actively preempting vehicle. Initially(prior to preemption), the threshold-lag factor 640 is zero percent(0%). When the threshold is crossed, the threshold-lag becomes itsmaximum value (i.e. 30%), and it is added to both the threshold-time andthe time-to-preempt factors for comparison to vehicle-ETA. Once avehicle has crossed the threshold, and the threshold-lag has beenexpanded, the threshold-lag linearly decreases back to zero percent (0%)over a small period (i.e. 10 seconds). This calculation is just one formof hysteresis (historical dependence) techniques used in the invention.

FIGS. 6, 7 and 8 are schematics that show detailed layouts of theintersection hardware components and, most specifically, multipleconfigurations for real-time monitoring of phasing/timing controllersignals. The configuration in FIG. 7 provides for interfacing to digitalBUS intersection controllers 20 b (such as NEMA TS1 controller models).The configuration in FIG. 8 provides for interfacing to analog-basedintersection controllers 20 c (such as type 170 controller models). Onsuch analog systems, traffic lights signals are monitored by afail-safe, isolated, high impedance tap and subsequent digital circuitprocessing. The monitor data is available for remote monitoring via thewide area communications and operations network. As shown in FIG. 6, thesystem is still compatible with controllers that disable monitoring 20 aor where monitoring is not desired.

Real-time monitor information is read and analyzed by the intersectionmonitor software task 610. These calculated values are forwarded to thepreempt monitor 600, where these intersection phasing values areintegrated with real-time vehicle information. The software attempts tooptimize preempt triggers with “time-to-preempt” calculations and“time-to-pedestrian-inhibit” calculations, as compared to the ETA of allapproaching emergency vehicles. The goal is to provide minimaldisruption to the nominal controller behavior and to maximize thethroughput of emergency vehicles through the preemption intersectionnetwork. Also, unlike other preemption systems, beyond simply sending apreempt command (actuating a preempt signal), the real-time monitorindependently measures the state of the controller-actuated trafficlight signals. This provides a critical closed-loop design: it assuresthat preempt commands are actually executed.

Real-time status monitor 42 is unique because it verifies the state ofthe traffic signals and sends the intersection status (i.e.“intersection preempted”, “conflict detected”, or “no preemption”) tointersection control module 10. That is, real-time status monitorreceives (i.e., “reads”) the output from traffic light controller 20 andpedestrian lights 22 a through 22 d and traffic lights 24 a through 24 dand transmits that information to intersection control module 10.Intersection control module 10 in turn relays that information toemergency vehicles via wireless RF transceiver 40 and antenna 41.Intersection control module 10 now sends signals to emergency displaypanels 45 a, 45 b, 45 c, and 45 d to light and flash large emergencysigns with the proper icons at each corner of an intersection showingthe position of any approaching emergency vehicle relative to thetraffic lanes of the intersection as shown and described in theabove-identified U.S. patent incorporated herein. The display panels 45a-45 d and proper icons used at each corner of an intersection are shownin FIG. 2 of the U.S. patent referenced hereinabove. The signage is alsoillustrated in U.S. Design Pat. No. 305,673, issued Jan. 23, 1990, andalso incorporated herein by reference.

Also, the real-time status monitor 42 provides which is transmitted viaRF master transceiver (or LAN) 60 and antenna 61 to a central monitoringsystem such as a dispatcher's office. Reciprocally, the intersectionreceives information on the state of its neighboring intersections. Thisclosed-loop architecture allows various units in the network toaccurately predict future movement, log critical information, and notifyusers of the system state.

The intersection control program 35 (specifically the preempt monitorsoftware task 600) uses map-matching techniques to compare vehiclenavigation and position estimates with the approach paths (cross-streetsstored locally as map vectors). This way the intersection can determineif any vehicle is on an inbound course towards the intersection by“snapping” it to the closest street. As an example, one of thecalculations is the “critical distance” test. This evaluates whether anapproaching car has statistically committed itself to crossing throughthe local intersection based on lack of turning options. Because of theknowledge of the road map, the intersection can preempt even when the“critical distance” is not line-of-sight. As an additional example, inthe event that any vehicle comes with a “warning distance” of theintersection (1000-ft commonly used), the control program 35 willactuate pedestrian-inhibit functions. Pedestrian lights 22 a through 22d are changed to prevent pedestrian traffic. Through a combination ofhysteresis-based (historical dependence) algorithms and dynamicproximity “windows”, the system is able to optimally route emergencyvehicles across the map grid. It is also able to effectively mitigatelossy communications, lossy navigation data, and other unpredictabledelays in the system.

Another improvement to the system is the provision of an audio warningto pedestrians. Thus simultaneously with controlling the lights andpedestrian flashing signals, controller 10 generates an audio message tobe delivered from audio warning device 50 to speakers 51 a through 51 d.

As mentioned, the details of the software in the intersection controlprogram for implementing the functions of the system are provided inAppendix B. Because the functions controlled are described in greatdetail in the text, many software solutions to implement the functionswill be apparent to those skilled in the art.

Emergency vehicle functions for the preemption system are illustrated inthe block diagram of FIG. 2. A transponder box 99 (and cables 98, 98 a)are installed in each emergency vehicle and provide the functions thatfacilitate communication with preempt-able intersections, otheremergency vehicles, and also central monitoring stations such as adispatching center. Inputs and outputs to and from the emergency vehiclesystem are handled by transponder control module 30 under the directionof proprietary control program software 15. Vehicle parameters aredetermined from several inputs provided to transponder control module30.

Vehicle position is available from GPS receiver 38 via antenna 39.Several positioning inputs 96 are available from ports in navigationinput device 34. Optional alternative inputs from ports and navigationinput device 34 are INU (inertial navigation and estimation unit 29)parameters including accelerometers, gyroscopes, wheel-tachometers, andheading indicators. Other inputs include ID tag tracking, beacontriangulation, modified traffic loop detectors, and others. Vehicleinformation such as speed and acceleration are read in real-time fromthe vehicle computer 33 using the on-board diagnostic (OBD) interfacecable and connector 33 a. These signals are converted and verified bythe OBD circuit board 32 and the translated digital signals are input totransponder control module 30 (embedded on a micro-controller 97).

The emergency vehicle transponder system communicates with intersectionsvia wireless RF transceiver 44 and antenna 45. The vehicles andintersections software task 670 running on the vehicle transponderhandles incoming intersection preempt alerts and vehicle positionreports from nearby units. It receives feedback verification anddisplays the information on-board by activating one or more LEDs 56, 57,or 58 on the LED display 54. If it receives a signal for safe passagethrough an intersection, “green” LED 56 is illuminated. If anotherhigh-priority emergency vehicle is concurrently trying to preempt thesame intersection, “yellow” LED 57 is illuminated. Illumination of “red”LED 58 indicates that there is no preemption at the intersection. LEDs56 through 58 are driven by “intersection preempted” logic circuit 55.Logic circuit 55 can also provide customized outputs to dynamic displaydevices 59, such as PC monitor displays (LCD's) and Personal DigitalAssistants (PDA's). Such devices are commonly used for law enforcementapplications within the vehicle. As mentioned, the operations softwareshown in FIG. 14 can be mobilized 80 and run on any vehicle-basedauxiliary hardware device with a standard operating system. The vehicleinterface software task 665 in the transponder control program allowsadvanced mapping and alerting of active nearby intersections andvehicles.

Emergency vehicle status is available in real time via master RFtransceiver 64 and antenna 65 to a central monitoring station. Thus theposition of any vehicle as well as the status at an intersection isalways available at some centrally located dispatch station.

As indicated previously, the software in control program 15 to implementthe functions of the transponder described above has many possiblesolutions. Thus the software provided to control the operation oftransponder control module 30 can be designed and implemented by anyoneskilled in the art given the detailed explanation of the system andfunctions described hereinabove. Also, as previously mentioned, AppendixB provides detailed pseudo-code of a full-featured version of thesoftware for both the intersection and vehicle.

FIG. 3 is a schematic block diagram of the transponder system mounted ineach vehicle. The transponder box 99 in the vehicle receives power fromcar battery through the OBD interface 33 a. The transponder box 99 has aGPS receiver such as that produced and manufactured by GarminInternational Incorporated. The transceiver can be a radio transceiverproduced and manufactured by Freewave Technologies of Boulder, Colo.

FIG. 4 is a schematic diagram of the on-board diagnostic (OBD) circuitfor the vehicle-based electronics and transponder. The on-boarddiagnostic circuit handles such information as speed, acceleration,heading, ignition status, etc. and generates the proper digital signals96 a for delivery to transponder control module 30.

FIG. 10 illustrates the general functionality of the vehicle transpondercontrol program software and firmware. The program monitors and logs allin-range vehicles and intersections and manages the data output to theoperator display. The core component of the transponder software is thenavigation prediction module software task 655. The task uses positionestimates by GPS and other absolute position inputs, and combines datafrom accelerometers, gyroscopes, tachometers, and heading indicators.This data is then integrated with historical logs. This process,commonly known as dead reckoning, uses accurate (yet possiblyintermittent) position reports integrated with time-based inertialnavigation data to generate enhanced position estimates. Positioninformation is forwarded to the transponder state and position monitorsoftware task 650. This task monitors vehicle state and diagnosticinputs (such as Code-3) and generates position/state reports tobroadcast via the wireless network.

FIG. 13 illustrates an example network topology for the communicationsand operations network. Emergency vehicles 300 and 301 send navigationreports (i.e. GPS) and other data/commands (via wireless connection)to/from intersections and other local vehicles. Preemption-equippedintersections 305, 306, and 307 monitor navigation information fromvehicles. Intersections cooperatively and redundantly communicate witheach other 320 (via wireless or LAN) to enhance data accuracy and ensurerobust communications. Data is also passed along to existing TMC(traffic management center) 330 using existing city LAN communicationsnetwork 325. If a LAN network is not used, wireless systems can besubstituted, such as through FMC 340 (fleet management center) systems.From there, FMC can forward all data to/from vehicle and TMC.

FIG. 14 is a block diagram of the operations software, designed for usein central command centers, mobile command stations, and in individualemergency vehicles. The diagram illustrates the primary functionalcomponents of the software. The primary components include algorithmicmodules and visual displays for: low-level data activity 405, priorityalerts 410, intersections' data 420, vehicles' data 430, and geographicmapping 450. In FIGS. 15, 16, and 17, both data and displays for thesecomponents are shown in an example preemption scenario. This exampledemonstrates the real-time operations monitoring of a conflict detectionscenario, whereby two police vehicles are approaching the sameintersection in high priority mode. FIG. 15 shows incoming data 461 fromvehicles and intersections within the preemption operationscommunications network 460. Textual status messages are provided on thedata status module display 405 a. The data status module 405 alsomaintains a historical record for all low-level communication anddata-flow activity. This module 405 relays all verified and prioritydata messages 406 (i.e. position, preempt, and conflict messages) to thealerts module 410. The alerts module display 410 a provides real-timevisual notifications of current high-priority events (i.e. active Code-3vehicles and preempted intersections) and enables rapid analysis of thecurrent preemption system status.

The alerts module 410 forwards all detailed data 411 to the vehicles andintersections modules 420 and 430. The intersection module display 420 ashows real-time detailed intersection data including the traffic lightstates 421 a (phasing) and pedestrian clearance states 421 b. Also shownare timing parameters 421 c (for example, minimum ETA to intersectionfor inbound direction) and display data (for example, visual warningsigns' states). The vehicle module display 430 a shows real-timedetailed vehicle data including estimated locations, car types,priority-states, navigation data (such as heading), and other historicalinformation.

All vehicles' and intersections' active data 411 is integrated andoverlaid on the mapping module display 450 a. The display is anadjustable city map with active units shown as icons, such as vehicleunits 431 a, 431 b and intersection units 432. Visual high-priorityalerts, such as conflict detection warnings 433, are logisticallyoverlaid on the map.

A secondary component of the operations software is used forinstallation and real-time configuration of units 470 as they are addedto the preemption network. For intersections, configuration commands 471include the upload of street grid databases, phase preemptioninformation, and enter/exit distance and timing. For vehicles,configuration commands 471 include ID tags, selection of vehicle type,and sensitivity settings for navigation algorithms. Various testutilities allow the installer to visually monitor the intersection andapproaching test vehicles. For instance, the system can be put into thesilent preempt mode (no warning signs), or can be manually activated topreempt without a vehicle. The software can communicate directly with alocal intersection or vehicle, or can use the local unit's transceiverto talk to the rest of the network.

The operations software can be used to analyze (and optimize) callresponse times and call response strategies (routes, etc.). It can beused from any location within the range of the network, and can also beintegrated into existing call-response centers. The software can also beused for emergency logistics management (i.e. multiple car responses),preventative warnings (i.e. conflict detection), and can also beintegrated into existing TMC incident management systems. The system anddisplays can be accessed via the internet 480 as well. Traffictechnicians can use the system to monitor phasing and optimize internalcontroller programming to match desired preemption settings andbehavior. The monitor software is also able to identify potentialproblems or conflicts in the network using intelligent “sniffer”software utilities. These algorithms watch incoming data to make surethat data is disseminated in real-time, that data is cohesive anderror-free, and that position/state reports are consistent. The systemalso has the capacity to quickly and autonomously shut off problemvehicle or intersection units. These utilities allow the system toquickly identify anomalies and request maintenance, thereby drasticallyreducing potentially significant traffic problems.

Thus there has been disclosed improvements to an emergency vehicletraffic signal preemption system. Improvements include providing anautonomous system that is not dependent on intersection being in visualrange. The system provides conflict detection and alerts emergencyvehicle operators in the area, and provides real-time monitoring of anintersection phase. The real-time monitoring of intersections isindicated by LEDs on a transponder or LCD display in the emergencyvehicle that show whether there is a conflict or the intersection beingapproached is not preempted. The system also includes the improvement ofan audio alarm to alert pedestrians who may not be aware of anapproaching emergency vehicle for various reasons or are at an anglewhere visible signs are not clear.

This invention is not to be limited by the embodiment shown in thedrawings and described in the description which is given by way ofexample and not of limitation, but only in accordance with the scope ofthe appended claims.

APPENDIX A

The following phrases and definitions are used to describepreemption-related terms, operator-configured parameters, andsoftware-derived calculations. These terms specifically relate to (a)the decision flow diagram in FIG. 11, (b) the example preemptionscenario shown in FIG. 12, and (c) the decision criteria used in theintersection preempt monitor software task:

General Definitions:

“Complete preemption” is the state where a preemption command has beensent to an intersection controller, and the command has been completedsuch that all PED and traffic lights are “red”, except the inboundtraffic light for a preempting emergency vehicle which is “green”.

“Street segment” is a line (vector) that when combined with othercontiguous street segments, represent a street map in the intersectioncontrol program software. The segments identify all local streets nearor crossing the intersection.

“Critical-inbound” refers to an emergency vehicle that is on a crossstreet segment, inbound based on its heading, and its ETA or proximitymake it eligible for preemption. A vehicle in this state, except inspecial circumstances, would be preempting the intersection.

“Hysteresis” is a historical dependence statistical calculation. It usesbehavior or rules formed while collecting previous time-based sequenceddata to predict future behavior. In the context of this preemptionsystem, hysteresis is used to address such observations as: “if ane-operator successfully preempts a traffic light, the intersectionprogram should be very conservative and cautious before discontinuingthe preemption for that vehicle.” This basic hysteresis approach isillustrated in FIGS. 11 and 12. Advanced approaches use tracking andprediction algorithms to more accurately assess vehicle position,e-operator intent, and optimize intersection controller behavior.

Operator-Configurable Values:

“Max-preempt-perimeter” is the maximum distance at which a vehicle isallowed to preempt the local intersection. As example, 3000-ft could beused.

“Street width” is the maximum deviation (distance) allowed between theline-center of a street segment and a vehicle's estimated position. Ifthe calculated difference is less than “street width”, the vehicle isconsidered “on” a street segment. As example, 50-ft could be used.

“Heading error” is the maximum deviation (angle) allowed between thedirection of a street segment and a vehicle's estimate heading. If thedifference between angles is less than the “heading error”, the vehicleis considered to be moving “along” that street segment. As example,15-degrees could be used.

“Critical distance” is the distance within which a vehicle isautomatically marked as critical-inbound (if heading meets criteria). Asexample, 200-ft could be used.

“Critical segment” is a boolean value that applies to all streetsegments; if “yes” then any vehicle “on” that street segment isautomatically marked as critical-inbound (if heading meets criteria).

“Max-PED-perimeter” is the distance within which pedestrian-inhibit isenabled to prevent standard PED clearance phases. As example, 2200-ftcould be used.

“Min-exit-distance” is the minimum outbound distance past which egressintersection-based warnings are allowed. As example, 30-ft could beused.

“Max-exit-distance” is the maximum outbound distance up to which egressintersection-based warnings are allowed. As example, 100-ft could beused.

“Min-exit-speed” is the minimum speed above which outboundintersection-based warnings are allowed. As example, 5-mph could beused.

“Min-preempt-speed” is the minimum speed above which inbound preemptionand inbound intersection-based warnings are allowed. As example, 10-mphcould be used.

“Max-latency” is the maximum time between preempt-able messages (seelatency-counter description) from the same vehicle before that vehicleis considered inactive. As example, 6-secs could be used.

Software Derived/Calculated Values:

“Max-NAV-error” is the maximum estimated distance error allowed forvehicle-ETA calculations, as determined by dead reckoning algorithms andpositioning device specifications. Any error exceeding this factor willinvalidate the associated estimated vehicle position. As example, 150-ftcould be used.

“Vehicle-ETA” is the minimum estimated ETA (estimated-time-of-arrival)of a vehicle at an intersection, as calculated using the real-time mapdistance between vehicle and intersection, vehicle speed, vehicleacceleration (based on historical averaging and vehicle type), streettype, and expected street conditions (i.e. time-of-day).

“Threshold-lag” is the minimum estimated time that thecomplete-preemption state must remain steady prior to a preemptingvehicle's arrival at an intersection. This calculation is based on thevehicle's speed. The purpose of this factor is to minimize slowing ofpreempting vehicle. The lag includes threshold-hysteresis (see below).

“Threshold-hysteresis” is a percentage time error included inthreshold-lag. When a vehicle preempts an intersection, thethreshold-hysteresis factor resets from 0% to a percentage of theinitial vehicle-ETA. For example, 30% could be the default initialsetting. Every second thereafter, this percentage is reduced linearly,until 0%. This ensures that once a vehicle is preempting, it is unlikelya temporary vehicle change will disable preemption (i.e. slowing down).

“Time-to-preempt” is the minimum time to achieve complete preemption atan intersection, estimated by the real-time phasing monitor. One of theprimary calculations to determine a vehicle's preempt eligibility is ifa vehicle's ETA is less than the sum of the time-to-preempt andthreshold-lag parameters.

“Latency-counter” is the number of seconds since the last “valid”preempt-able message was received from a given vehicle. Some criteriathat would cause the latency counter to increment are: (a) a positionreport accuracy worse than Max-NAV-error, (b) vehicle not “on” a streetsegment, (c) low or no vehicle speed, or (d) vehicle heading notinbound.

1. An emergency vehicle traffic control system comprising: a processor;and a memory operably coupled to the processor and having programinstructions stored therein, the processor being operable to execute theprogram instructions, the program instructions including: receivingnavigation information of an emergency vehicle approaching anintersection equipped with one or more vehicular traffic lights and oneor more pedestrian traffic lights; estimating a time of arrival at theintersection based on the navigation information; and controlling thevehicular traffic lights and the one or more pedestrian traffic lightsbased on the estimated time of arrival and current light states of thevehicular traffic lights and the pedestrian traffic lights for providingright of way to the emergency vehicle.
 2. The system of claim 1 furthercomprising: a warning alert control module at the intersection foractivation of a warning message associated with the approachingemergency vehicle.
 3. The system of claim 2, wherein the warning messageis a visual alert.
 4. The system of claim 2, wherein the warning messageis an audio alert.
 5. The system of claim 1, wherein the programinstructions further include: assigning a preemption priority to theemergency vehicle.
 6. The system of claim 1, wherein the programinstructions further include: transmitting a preemption status to theemergency vehicle.
 7. The system of claim 1, wherein the programinstructions further include: monitoring status of the vehicular trafficlights and the one or more pedestrian traffic lights for verifyingpreemption of the vehicular traffic lights and the one or morepedestrian traffic lights.
 8. The system of claim 1, wherein thenavigation information includes emergency vehicle position data.
 9. Thesystem of claim 8, wherein the position data is derived from an inertialnavigation unit.
 10. The system of claim 8, wherein the position data isderived from a global positioning system.
 11. The system of claim 1,wherein the controlling is based on a time for a pedestrian to cross theintersection.
 12. The system of claim 1, wherein the controlling of thepedestrian traffic lights includes inhibiting a pedestrian clearancephase.
 13. The system claim 12, wherein inhibiting the pedestrianclearance phase includes disabling a pedestrian call button.